how to check if an object exists in the database and then insert it into a form in django

I have the following model:models.py

name = models.CharField(max_length=100, blank=False, null=False)
serial_number = models.CharField(max_length=100, blank=False, null=False)
make = models.CharField(max_length=100, blank=False, null=False)
model = models.CharField(max_length=100, blank=False, null=False)
color= models.CharField(max_length=100, blank=False, null=False)
date_acquired = models.DateTimeField(auto_created=True)
acquired_from = models.CharField(max_length=100, choices=ACQUIRED_FROM)
holder = models.ForeignKey(CertificateHolder, blank=False,)
dealer_license = models.ForeignKey(Dealer, blank=False)

I have created a form using ModelForm like this:

class IssueItemForm(ModelForm):

class Meta:
    model = IssuedItem
    fields = '__all__'

A dealer needs to check if a certificate Holder exists before issuing the item, My code for that looks like this;

views.py:

def search(request):
try:
    query = request.GET.get('q')
    results = 0

except ValueError:
    query = None
    results = None
if query:
    results = CertificateHolder.objects.get(cert_no=query)

context = RequestContext(request)

return render_to_response('core/results.html', {"results": results, }, context_instance=context)

Then I have templates search.html and results.html

<form method="get" action="/search/">
<input type="text" name="q" id="id_q" value="{{ query }}"/>
<input type="submit" value="Search" />
</form>

In results.html I have

{% if results %}
<h3>The Certificate number is valid</h3>
<h3>To issues an item click the button below</h3>
<a href="{% url 'issueitem' %}">Issue A New Item</a>

{% else %}
<h3 class='error'>Please enter a valid Certificate</h3>
<form method="get" action="/search/">
  <input type="text" name="q" id="id_q" value="{{ query }}"/>
  <input type="submit" value="Search" />
</form>

{% endif %}

The code works if there is a certificate in the database but if there is no match it throws an error like this:

error image

However I would like the error to be part of the code to tell the dealer that that number does not exist and that he should try another. Also when a certificate exists I would like it to be inserted into the holder field instead of fetching from the database like it is doing now. Where am i going wrong?